1. Field of the Invention
The present invention relates to a laser power-supply device, and in particular, relates to a laser power-supply device that is inexpensive and little-affected by breakage.
2. Description of the Related Art
A laser power-supply device has a light-emitting unit (cavity unit) that supplies excitation light to a laser oscillator, and a power-supply unit for supplying a current to the cavity unit and controlling light emission of a plurality of light-emitting elements. The cavity unit generally has a plurality of light-emitting elements. As a circuit configuration of the power-supply unit, a switching regulator composed of a rectifier circuit, a switching circuit, a smoothing circuit, a current detection circuit, and a control circuit is known. Circuit components of the switching regulator are mounted on a printed circuit board, the printed circuit board is surrounded by a housing frame, and repair and replacement at the time of manufacture or breakage of the laser power-supply device are performed for each of the power-supply unit. In the laser power-supply device, after a voltage (for example, AC 200 V) to be supplied to a voltage input unit of the power-supply unit is rectified by the rectifier circuit, the voltage is converted to a DC voltage by the switching circuit and the smoothing circuit, a current is supplied to the plurality of light-emitting elements of the cavity unit, and a current value thereof is detected by the current detection circuit. The current value is feedback-controlled to be constant with respect to a current command value from a current command unit.
Generally, in a light-emitting element such as an LED or a semiconductor laser, light intensity (light power) to be outputted varies in accordance with a current. Since characteristics of a voltage between terminals (forward voltage) Vf of a light-emitting element vary in accordance with environmental factors such as a production tolerance and a temperature, the light power is controlled by controlling the current supplied to the cavity unit from the power-supply unit.
When an AC input voltage in the power-supply unit is A, and a forward voltage of the light-emitting element is Vf, the number N of the light-emitting elements that can be connected in series in the cavity unit needs to satisfy A×21/2≧Vf×N. Thus, in order to increase the number of the light-emitting elements so as to obtain desired light power, the light-emitting elements need to be connected in parallel. Generally, failure of a light-emitting element is due to a short circuit. Thus, in this configuration, there was a problem in that the operation of the device is stopped when any one of the light-emitting elements is broken (short-circuits).
Japanese Unexamined Patent Publication (Kokai) No. 2013-175562 describes a laser power-supply device having a main circuit that supplies a principal current for laser output to a lamp, and a simmer circuit that supplies a simmer current, and a configuration in which a switching loss is reduced, and a printed circuit board is not broken even when a semiconductor element fails. Japanese Unexamined Patent Publication (Kokai) No. 2013-175562 does not describe a plurality of light-emitting element rows, and the simmer circuit described in Japanese Unexamined Patent Publication (Kokai) No. 2013-175562 is a circuit fundamentally different from the main circuit.
Japanese Unexamined Patent Publication (Kokai) No. 2014-232692 describes a technique in which switching regulators are configured in series in two stages in a control device including an electronic transformer for a low-voltage halogen lamp such that the control device stably behaves even when a luminaire for turning on a light-emitting element is connected thereto. Japanese Unexamined Patent Publication (Kokai) No. 2014-232692 does not describe a plurality of light-emitting element rows.
It is desired that, in a laser power-supply device, the number of light-emitting elements to be mounted can be easily increased, and the device can continue to operate even when any one of the light-emitting elements is broken (short-circuits).